/*
 * Copyright (C) 2006 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.reflect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.Beta;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ForwardingSet;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;
import com.google.common.primitives.Primitives;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * A {@link Type} with generics.
 *
 * <p>
 * Operations that are otherwise only available in {@link Class} are implemented to support
 * {@code Type}, for example {@link #isSubtypeOf}, {@link #isArray} and {@link #getComponentType}.
 * It also provides additional utilities such as {@link #getTypes}, {@link #resolveType}, etc.
 *
 * <p>
 * There are three ways to get a {@code TypeToken} instance:
 *
 * <ul>
 *
 * <li>Wrap a {@code Type} obtained via reflection. For example:
 * {@code TypeToken.of(method.getGenericReturnType())}.
 *
 * <li>Capture a generic type with a (usually anonymous) subclass. For example:
 * 
 * <pre>
 *    {@code
 *   new TypeToken<List<String>>() {}}
 * </pre>
 *
 * <p>
 * Note that it's critical that the actual type argument is carried by a subclass. The following
 * code is wrong because it only captures the {@code <T>} type variable of the {@code
 *     listType()} method signature; while {@code <String>} is lost in erasure:
 *
 * <pre>
 * {
 *     &#64;code
 *     class Util {
 *         static <T> TypeToken<List<T>> listType() {
 *             return new TypeToken<List<T>>() {};
 *         }
 *     }
 *
 *     TypeToken<List<String>> stringListType = Util.<String>listType();
 * }
 * </pre>
 *
 * <li>Capture a generic type with a (usually anonymous) subclass and resolve it against a context
 * class that knows what the type parameters are. For example:
 * 
 * <pre>
 *    {@code
 *   abstract class IKnowMyType<T> {
 *     TypeToken<T> type = new TypeToken<T>(getClass()) {};
 *   }
 *   new IKnowMyType<String>() {}.type => String}
 * </pre>
 *
 * </ul>
 *
 * <p>
 * {@code TypeToken} is serializable when no type variable is contained in the type.
 *
 * <p>
 * Note to Guice users: {@code} TypeToken is similar to Guice's {@code TypeLiteral} class except
 * that it is serializable and offers numerous additional utility methods.
 *
 * @author Bob Lee
 * @author Sven Mawson
 * @author Ben Yu
 * @since 12.0
 */
@Beta
@SuppressWarnings("serial") // SimpleTypeToken is the serialized form.
public abstract class TypeToken<T> extends TypeCapture<T> implements Serializable {

    private final Type runtimeType;

    /** Resolver for resolving types with {@link #runtimeType} as context. */
    private transient TypeResolver typeResolver;

    /**
     * Constructs a new type token of {@code T}.
     *
     * <p>
     * Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
     * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
     *
     * <p>
     * For example:
     * 
     * <pre>
     * {
     *     &#64;code
     *     TypeToken<List<String>> t = new TypeToken<List<String>>() {};
     * }
     * </pre>
     */
    protected TypeToken() {
        this.runtimeType = capture();
        checkState(!(runtimeType instanceof TypeVariable), "Cannot construct a TypeToken for a type variable.\n"
                + "You probably meant to call new TypeToken<%s>(getClass()) "
                + "that can resolve the type variable for you.\n"
                + "If you do need to create a TypeToken of a type variable, " + "please use TypeToken.of() instead.",
                runtimeType);
    }

    /**
     * Constructs a new type token of {@code T} while resolving free type variables in the context
     * of {@code declaringClass}.
     *
     * <p>
     * Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
     * anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
     *
     * <p>
     * For example:
     * 
     * <pre>
     *    {@code
     *   abstract class IKnowMyType<T> {
     *     TypeToken<T> getMyType() {
     *       return new TypeToken<T>(getClass()) {};
     *     }
     *   }
     *
     *   new IKnowMyType<String>() {}.getMyType() => String}
     * </pre>
     */
    protected TypeToken(Class<?> declaringClass) {
        Type captured = super.capture();
        if (captured instanceof Class) {
            this.runtimeType = captured;
        } else {
            this.runtimeType = of(declaringClass).resolveType(captured).runtimeType;
        }
    }

    private TypeToken(Type type) {
        this.runtimeType = checkNotNull(type);
    }

    /** Returns an instance of type token that wraps {@code type}. */
    public static <T> TypeToken<T> of(Class<T> type) {
        return new SimpleTypeToken<T>(type);
    }

    /** Returns an instance of type token that wraps {@code type}. */
    public static TypeToken<?> of(Type type) {
        return new SimpleTypeToken<Object>(type);
    }

    /**
     * Returns the raw type of {@code T}. Formally speaking, if {@code T} is returned by
     * {@link java.lang.reflect.Method#getGenericReturnType}, the raw type is what's returned by
     * {@link java.lang.reflect.Method#getReturnType} of the same method object. Specifically:
     * <ul>
     * <li>If {@code T} is a {@code Class} itself, {@code T} itself is returned.
     * <li>If {@code T} is a {@link ParameterizedType}, the raw type of the parameterized type is
     * returned.
     * <li>If {@code T} is a {@link GenericArrayType}, the returned type is the corresponding array
     * class. For example: {@code List<Integer>[] => List[]}.
     * <li>If {@code T} is a type variable or a wildcard type, the raw type of the first upper bound
     * is returned. For example: {@code <X extends Foo> => Foo}.
     * </ul>
     */
    public final Class<? super T> getRawType() {
        // For wildcard or type variable, the first bound determines the runtime type.
        Class<?> rawType = getRawTypes().iterator().next();
        @SuppressWarnings("unchecked") // raw type is |T|
        Class<? super T> result = (Class<? super T>) rawType;
        return result;
    }

    /** Returns the represented type. */
    public final Type getType() {
        return runtimeType;
    }

    /**
     * <p>
     * Returns a new {@code TypeToken} where type variables represented by {@code typeParam} are
     * substituted by {@code typeArg}. For example, it can be used to construct {@code Map<K, V>}
     * for any {@code K} and {@code V} type:
     * 
     * <pre>
     *    {@code
     *   static <K, V> TypeToken<Map<K, V>> mapOf(
     *       TypeToken<K> keyType, TypeToken<V> valueType) {
     *     return new TypeToken<Map<K, V>>() {}
     *         .where(new TypeParameter<K>() {}, keyType)
     *         .where(new TypeParameter<V>() {}, valueType);
     *   }}
     * </pre>
     *
     * @param <X> The parameter type
     * @param typeParam the parameter type variable
     * @param typeArg the actual type to substitute
     */
    public final <X> TypeToken<T> where(TypeParameter<X> typeParam, TypeToken<X> typeArg) {
        TypeResolver resolver = new TypeResolver()
                .where(ImmutableMap.of(new TypeResolver.TypeVariableKey(typeParam.typeVariable), typeArg.runtimeType));
        // If there's any type error, we'd report now rather than later.
        return new SimpleTypeToken<T>(resolver.resolveType(runtimeType));
    }

    /**
     * <p>
     * Returns a new {@code TypeToken} where type variables represented by {@code typeParam} are
     * substituted by {@code typeArg}. For example, it can be used to construct {@code Map<K, V>}
     * for any {@code K} and {@code V} type:
     * 
     * <pre>
     *    {@code
     *   static <K, V> TypeToken<Map<K, V>> mapOf(
     *       Class<K> keyType, Class<V> valueType) {
     *     return new TypeToken<Map<K, V>>() {}
     *         .where(new TypeParameter<K>() {}, keyType)
     *         .where(new TypeParameter<V>() {}, valueType);
     *   }}
     * </pre>
     *
     * @param <X> The parameter type
     * @param typeParam the parameter type variable
     * @param typeArg the actual type to substitute
     */
    public final <X> TypeToken<T> where(TypeParameter<X> typeParam, Class<X> typeArg) {
        return where(typeParam, of(typeArg));
    }

    /**
     * <p>
     * Resolves the given {@code type} against the type context represented by this type. For
     * example:
     * 
     * <pre>
     *    {@code
     *   new TypeToken<List<String>>() {}.resolveType(
     *       List.class.getMethod("get", int.class).getGenericReturnType())
     *   => String.class}
     * </pre>
     */
    public final TypeToken<?> resolveType(Type type) {
        checkNotNull(type);
        TypeResolver resolver = typeResolver;
        if (resolver == null) {
            resolver = (typeResolver = TypeResolver.accordingTo(runtimeType));
        }
        return of(resolver.resolveType(type));
    }

    private Type[] resolveInPlace(Type[] types) {
        for (int i = 0; i < types.length; i++) {
            types[i] = resolveType(types[i]).getType();
        }
        return types;
    }

    private TypeToken<?> resolveSupertype(Type type) {
        TypeToken<?> supertype = resolveType(type);
        // super types' type mapping is a subset of type mapping of this type.
        supertype.typeResolver = typeResolver;
        return supertype;
    }

    /**
     * Returns the generic superclass of this type or {@code null} if the type represents
     * {@link Object} or an interface. This method is similar but different from
     * {@link Class#getGenericSuperclass}. For example, {@code new TypeToken<StringArrayList>()
     * {}.getGenericSuperclass()} will return {@code new TypeToken<ArrayList<String>>() {}}; while
     * {@code StringArrayList.class.getGenericSuperclass()} will return {@code ArrayList<E>}, where
     * {@code E} is the type variable declared by class {@code ArrayList}.
     *
     * <p>
     * If this type is a type variable or wildcard, its first upper bound is examined and returned
     * if the bound is a class or extends from a class. This means that the returned type could be a
     * type variable too.
     */
    @Nullable
    final TypeToken<? super T> getGenericSuperclass() {
        if (runtimeType instanceof TypeVariable) {
            // First bound is always the super class, if one exists.
            return boundAsSuperclass(((TypeVariable<?>) runtimeType).getBounds()[0]);
        }
        if (runtimeType instanceof WildcardType) {
            // wildcard has one and only one upper bound.
            return boundAsSuperclass(((WildcardType) runtimeType).getUpperBounds()[0]);
        }
        Type superclass = getRawType().getGenericSuperclass();
        if (superclass == null) {
            return null;
        }
        @SuppressWarnings("unchecked") // super class of T
        TypeToken<? super T> superToken = (TypeToken<? super T>) resolveSupertype(superclass);
        return superToken;
    }

    @Nullable
    private TypeToken<? super T> boundAsSuperclass(Type bound) {
        TypeToken<?> token = of(bound);
        if (token.getRawType().isInterface()) {
            return null;
        }
        @SuppressWarnings("unchecked") // only upper bound of T is passed in.
        TypeToken<? super T> superclass = (TypeToken<? super T>) token;
        return superclass;
    }

    /**
     * Returns the generic interfaces that this type directly {@code implements}. This method is
     * similar but different from {@link Class#getGenericInterfaces()}. For example, {@code new
     * TypeToken<List<String>>() {}.getGenericInterfaces()} will return a list that contains
     * {@code new TypeToken<Iterable<String>>() {}}; while {@code List.class.getGenericInterfaces()}
     * will return an array that contains {@code Iterable<T>}, where the {@code T} is the type
     * variable declared by interface {@code Iterable}.
     *
     * <p>
     * If this type is a type variable or wildcard, its upper bounds are examined and those that are
     * either an interface or upper-bounded only by interfaces are returned. This means that the
     * returned types could include type variables too.
     */
    final ImmutableList<TypeToken<? super T>> getGenericInterfaces() {
        if (runtimeType instanceof TypeVariable) {
            return boundsAsInterfaces(((TypeVariable<?>) runtimeType).getBounds());
        }
        if (runtimeType instanceof WildcardType) {
            return boundsAsInterfaces(((WildcardType) runtimeType).getUpperBounds());
        }
        ImmutableList.Builder<TypeToken<? super T>> builder = ImmutableList.builder();
        for (Type interfaceType : getRawType().getGenericInterfaces()) {
            @SuppressWarnings("unchecked") // interface of T
            TypeToken<? super T> resolvedInterface = (TypeToken<? super T>) resolveSupertype(interfaceType);
            builder.add(resolvedInterface);
        }
        return builder.build();
    }

    private ImmutableList<TypeToken<? super T>> boundsAsInterfaces(Type[] bounds) {
        ImmutableList.Builder<TypeToken<? super T>> builder = ImmutableList.builder();
        for (Type bound : bounds) {
            @SuppressWarnings("unchecked") // upper bound of T
            TypeToken<? super T> boundType = (TypeToken<? super T>) of(bound);
            if (boundType.getRawType().isInterface()) {
                builder.add(boundType);
            }
        }
        return builder.build();
    }

    /**
     * Returns the set of interfaces and classes that this type is or is a subtype of. The returned
     * types are parameterized with proper type arguments.
     *
     * <p>
     * Subtypes are always listed before supertypes. But the reverse is not true. A type isn't
     * necessarily a subtype of all the types following. Order between types without subtype
     * relationship is arbitrary and not guaranteed.
     *
     * <p>
     * If this type is a type variable or wildcard, upper bounds that are themselves type variables
     * aren't included (their super interfaces and superclasses are).
     */
    public final TypeSet getTypes() {
        return new TypeSet();
    }

    /**
     * Returns the generic form of {@code superclass}. For example, if this is
     * {@code ArrayList<String>}, {@code Iterable<String>} is returned given the input
     * {@code Iterable.class}.
     */
    public final TypeToken<? super T> getSupertype(Class<? super T> superclass) {
        checkArgument(this.someRawTypeIsSubclassOf(superclass), "%s is not a super class of %s", superclass, this);
        if (runtimeType instanceof TypeVariable) {
            return getSupertypeFromUpperBounds(superclass, ((TypeVariable<?>) runtimeType).getBounds());
        }
        if (runtimeType instanceof WildcardType) {
            return getSupertypeFromUpperBounds(superclass, ((WildcardType) runtimeType).getUpperBounds());
        }
        if (superclass.isArray()) {
            return getArraySupertype(superclass);
        }
        @SuppressWarnings("unchecked") // resolved supertype
        TypeToken<? super T> supertype = (TypeToken<? super T>) resolveSupertype(toGenericType(superclass).runtimeType);
        return supertype;
    }

    /**
     * Returns subtype of {@code this} with {@code subclass} as the raw class. For example, if this
     * is {@code Iterable<String>} and {@code subclass} is {@code List}, {@code List<String>} is
     * returned.
     */
    public final TypeToken<? extends T> getSubtype(Class<?> subclass) {
        checkArgument(!(runtimeType instanceof TypeVariable), "Cannot get subtype of type variable <%s>", this);
        if (runtimeType instanceof WildcardType) {
            return getSubtypeFromLowerBounds(subclass, ((WildcardType) runtimeType).getLowerBounds());
        }
        // unwrap array type if necessary
        if (isArray()) {
            return getArraySubtype(subclass);
        }
        // At this point, it's either a raw class or parameterized type.
        checkArgument(getRawType().isAssignableFrom(subclass), "%s isn't a subclass of %s", subclass, this);
        Type resolvedTypeArgs = resolveTypeArgsForSubclass(subclass);
        @SuppressWarnings("unchecked") // guarded by the isAssignableFrom() statement above
        TypeToken<? extends T> subtype = (TypeToken<? extends T>) of(resolvedTypeArgs);
        return subtype;
    }

    /**
     * Returns true if this type is a supertype of the given {@code type}. "Supertype" is defined
     * according to
     * <a href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for
     * type arguments</a> introduced with Java generics.
     *
     * @since 19.0
     */
    public final boolean isSupertypeOf(TypeToken<?> type) {
        return type.isSubtypeOf(getType());
    }

    /**
     * Returns true if this type is a supertype of the given {@code type}. "Supertype" is defined
     * according to
     * <a href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for
     * type arguments</a> introduced with Java generics.
     *
     * @since 19.0
     */
    public final boolean isSupertypeOf(Type type) {
        return of(type).isSubtypeOf(getType());
    }

    /**
     * Returns true if this type is a subtype of the given {@code type}. "Subtype" is defined
     * according to
     * <a href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for
     * type arguments</a> introduced with Java generics.
     *
     * @since 19.0
     */
    public final boolean isSubtypeOf(TypeToken<?> type) {
        return isSubtypeOf(type.getType());
    }

    /**
     * Returns true if this type is a subtype of the given {@code type}. "Subtype" is defined
     * according to
     * <a href="http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.5.1">the rules for
     * type arguments</a> introduced with Java generics.
     *
     * @since 19.0
     */
    public final boolean isSubtypeOf(Type supertype) {
        checkNotNull(supertype);
        if (supertype instanceof WildcardType) {
            // if 'supertype' is <? super Foo>, 'this' can be:
            // Foo, SubFoo, <? extends Foo>.
            // if 'supertype' is <? extends Foo>, nothing is a subtype.
            return any(((WildcardType) supertype).getLowerBounds()).isSupertypeOf(runtimeType);
        }
        // if 'this' is wildcard, it's a suptype of to 'supertype' if any of its "extends"
        // bounds is a subtype of 'supertype'.
        if (runtimeType instanceof WildcardType) {
            // <? super Base> is of no use in checking 'from' being a subtype of 'to'.
            return any(((WildcardType) runtimeType).getUpperBounds()).isSubtypeOf(supertype);
        }
        // if 'this' is type variable, it's a subtype if any of its "extends"
        // bounds is a subtype of 'supertype'.
        if (runtimeType instanceof TypeVariable) {
            return runtimeType.equals(supertype)
                    || any(((TypeVariable<?>) runtimeType).getBounds()).isSubtypeOf(supertype);
        }
        if (runtimeType instanceof GenericArrayType) {
            return of(supertype).isSupertypeOfArray((GenericArrayType) runtimeType);
        }
        // Proceed to regular Type subtype check
        if (supertype instanceof Class) {
            return this.someRawTypeIsSubclassOf((Class<?>) supertype);
        } else if (supertype instanceof ParameterizedType) {
            return this.isSubtypeOfParameterizedType((ParameterizedType) supertype);
        } else if (supertype instanceof GenericArrayType) {
            return this.isSubtypeOfArrayType((GenericArrayType) supertype);
        } else { // to instanceof TypeVariable
            return false;
        }
    }

    /**
     * Returns true if this type is known to be an array type, such as {@code int[]}, {@code T[]},
     * {@code <? extends Map<String, Integer>[]>} etc.
     */
    public final boolean isArray() {
        return getComponentType() != null;
    }

    /**
     * Returns true if this type is one of the nine primitive types (including {@code void}).
     *
     * @since 15.0
     */
    public final boolean isPrimitive() {
        return (runtimeType instanceof Class) && ((Class<?>) runtimeType).isPrimitive();
    }

    /**
     * Returns the corresponding wrapper type if this is a primitive type; otherwise returns
     * {@code this} itself. Idempotent.
     *
     * @since 15.0
     */
    public final TypeToken<T> wrap() {
        if (isPrimitive()) {
            @SuppressWarnings("unchecked") // this is a primitive class
            Class<T> type = (Class<T>) runtimeType;
            return of(Primitives.wrap(type));
        }
        return this;
    }

    private boolean isWrapper() {
        return Primitives.allWrapperTypes().contains(runtimeType);
    }

    /**
     * Returns the corresponding primitive type if this is a wrapper type; otherwise returns
     * {@code this} itself. Idempotent.
     *
     * @since 15.0
     */
    public final TypeToken<T> unwrap() {
        if (isWrapper()) {
            @SuppressWarnings("unchecked") // this is a wrapper class
            Class<T> type = (Class<T>) runtimeType;
            return of(Primitives.unwrap(type));
        }
        return this;
    }

    /**
     * Returns the array component type if this type represents an array ({@code int[]},
     * {@code T[]}, {@code <? extends Map<String, Integer>[]>} etc.), or else {@code null} is
     * returned.
     */
    @Nullable
    public final TypeToken<?> getComponentType() {
        Type componentType = Types.getComponentType(runtimeType);
        if (componentType == null) {
            return null;
        }
        return of(componentType);
    }

    /**
     * Returns the {@link Invokable} for {@code method}, which must be a member of {@code T}.
     *
     * @since 14.0
     */
    public final Invokable<T, Object> method(Method method) {
        checkArgument(this.someRawTypeIsSubclassOf(method.getDeclaringClass()), "%s not declared by %s", method, this);
        return new Invokable.MethodInvokable<T>(method) {
            @Override
            Type getGenericReturnType() {
                return resolveType(super.getGenericReturnType()).getType();
            }

            @Override
            Type[] getGenericParameterTypes() {
                return resolveInPlace(super.getGenericParameterTypes());
            }

            @Override
            Type[] getGenericExceptionTypes() {
                return resolveInPlace(super.getGenericExceptionTypes());
            }

            @Override
            public TypeToken<T> getOwnerType() {
                return TypeToken.this;
            }

            @Override
            public String toString() {
                return getOwnerType() + "." + super.toString();
            }
        };
    }

    /**
     * Returns the {@link Invokable} for {@code constructor}, which must be a member of {@code T}.
     *
     * @since 14.0
     */
    public final Invokable<T, T> constructor(Constructor<?> constructor) {
        checkArgument(constructor.getDeclaringClass() == getRawType(), "%s not declared by %s", constructor,
                getRawType());
        return new Invokable.ConstructorInvokable<T>(constructor) {
            @Override
            Type getGenericReturnType() {
                return resolveType(super.getGenericReturnType()).getType();
            }

            @Override
            Type[] getGenericParameterTypes() {
                return resolveInPlace(super.getGenericParameterTypes());
            }

            @Override
            Type[] getGenericExceptionTypes() {
                return resolveInPlace(super.getGenericExceptionTypes());
            }

            @Override
            public TypeToken<T> getOwnerType() {
                return TypeToken.this;
            }

            @Override
            public String toString() {
                return getOwnerType() + "(" + Joiner.on(", ").join(getGenericParameterTypes()) + ")";
            }
        };
    }

    /**
     * The set of interfaces and classes that {@code T} is or is a subtype of. {@link Object} is not
     * included in the set if this type is an interface.
     */
    public class TypeSet extends ForwardingSet<TypeToken<? super T>> implements Serializable {

        private transient ImmutableSet<TypeToken<? super T>> types;

        TypeSet() {}

        /** Returns the types that are interfaces implemented by this type. */
        public TypeSet interfaces() {
            return new InterfaceSet(this);
        }

        /** Returns the types that are classes. */
        public TypeSet classes() {
            return new ClassSet();
        }

        @Override
        protected Set<TypeToken<? super T>> delegate() {
            ImmutableSet<TypeToken<? super T>> filteredTypes = types;
            if (filteredTypes == null) {
                // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
                @SuppressWarnings({"unchecked", "rawtypes"})
                ImmutableList<TypeToken<? super T>> collectedTypes =
                        (ImmutableList) TypeCollector.FOR_GENERIC_TYPE.collectTypes(TypeToken.this);
                return (types = FluentIterable.from(collectedTypes).filter(TypeFilter.IGNORE_TYPE_VARIABLE_OR_WILDCARD)
                        .toSet());
            } else {
                return filteredTypes;
            }
        }

        /** Returns the raw types of the types in this set, in the same order. */
        public Set<Class<? super T>> rawTypes() {
            // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
            @SuppressWarnings({"unchecked", "rawtypes"})
            ImmutableList<Class<? super T>> collectedTypes =
                    (ImmutableList) TypeCollector.FOR_RAW_TYPE.collectTypes(getRawTypes());
            return ImmutableSet.copyOf(collectedTypes);
        }

        private static final long serialVersionUID = 0;
    }

    private final class InterfaceSet extends TypeSet {

        private final transient TypeSet allTypes;
        private transient ImmutableSet<TypeToken<? super T>> interfaces;

        InterfaceSet(TypeSet allTypes) {
            this.allTypes = allTypes;
        }

        @Override
        protected Set<TypeToken<? super T>> delegate() {
            ImmutableSet<TypeToken<? super T>> result = interfaces;
            if (result == null) {
                return (interfaces = FluentIterable.from(allTypes).filter(TypeFilter.INTERFACE_ONLY).toSet());
            } else {
                return result;
            }
        }

        @Override
        public TypeSet interfaces() {
            return this;
        }

        @Override
        public Set<Class<? super T>> rawTypes() {
            // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
            @SuppressWarnings({"unchecked", "rawtypes"})
            ImmutableList<Class<? super T>> collectedTypes =
                    (ImmutableList) TypeCollector.FOR_RAW_TYPE.collectTypes(getRawTypes());
            return FluentIterable.from(collectedTypes).filter(new Predicate<Class<?>>() {
                @Override
                public boolean apply(Class<?> type) {
                    return type.isInterface();
                }
            }).toSet();
        }

        @Override
        public TypeSet classes() {
            throw new UnsupportedOperationException("interfaces().classes() not supported.");
        }

        private Object readResolve() {
            return getTypes().interfaces();
        }

        private static final long serialVersionUID = 0;
    }

    private final class ClassSet extends TypeSet {

        private transient ImmutableSet<TypeToken<? super T>> classes;

        @Override
        protected Set<TypeToken<? super T>> delegate() {
            ImmutableSet<TypeToken<? super T>> result = classes;
            if (result == null) {
                @SuppressWarnings({"unchecked", "rawtypes"})
                ImmutableList<TypeToken<? super T>> collectedTypes =
                        (ImmutableList) TypeCollector.FOR_GENERIC_TYPE.classesOnly().collectTypes(TypeToken.this);
                return (classes = FluentIterable.from(collectedTypes)
                        .filter(TypeFilter.IGNORE_TYPE_VARIABLE_OR_WILDCARD).toSet());
            } else {
                return result;
            }
        }

        @Override
        public TypeSet classes() {
            return this;
        }

        @Override
        public Set<Class<? super T>> rawTypes() {
            // Java has no way to express ? super T when we parameterize TypeToken vs. Class.
            @SuppressWarnings({"unchecked", "rawtypes"})
            ImmutableList<Class<? super T>> collectedTypes =
                    (ImmutableList) TypeCollector.FOR_RAW_TYPE.classesOnly().collectTypes(getRawTypes());
            return ImmutableSet.copyOf(collectedTypes);
        }

        @Override
        public TypeSet interfaces() {
            throw new UnsupportedOperationException("classes().interfaces() not supported.");
        }

        private Object readResolve() {
            return getTypes().classes();
        }

        private static final long serialVersionUID = 0;
    }

    private enum TypeFilter implements Predicate<TypeToken<?>> {
        IGNORE_TYPE_VARIABLE_OR_WILDCARD {
            @Override
            public boolean apply(TypeToken<?> type) {
                return !(type.runtimeType instanceof TypeVariable || type.runtimeType instanceof WildcardType);
            }
        },
        INTERFACE_ONLY {
            @Override
            public boolean apply(TypeToken<?> type) {
                return type.getRawType().isInterface();
            }
        }
    }

    /**
     * Returns true if {@code o} is another {@code TypeToken} that represents the same {@link Type}.
     */
    @Override
    public boolean equals(@Nullable Object o) {
        if (o instanceof TypeToken) {
            TypeToken<?> that = (TypeToken<?>) o;
            return runtimeType.equals(that.runtimeType);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return runtimeType.hashCode();
    }

    @Override
    public String toString() {
        return Types.toString(runtimeType);
    }

    /** Implemented to support serialization of subclasses. */
    protected Object writeReplace() {
        // TypeResolver just transforms the type to our own impls that are Serializable
        // except TypeVariable.
        return of(new TypeResolver().resolveType(runtimeType));
    }

    /**
     * Ensures that this type token doesn't contain type variables, which can cause unchecked type
     * errors for callers like {@link TypeToInstanceMap}.
     */
    @CanIgnoreReturnValue
    final TypeToken<T> rejectTypeVariables() {
        new TypeVisitor() {
            @Override
            void visitTypeVariable(TypeVariable<?> type) {
                throw new IllegalArgumentException(
                        runtimeType + "contains a type variable and is not safe for the operation");
            }

            @Override
            void visitWildcardType(WildcardType type) {
                visit(type.getLowerBounds());
                visit(type.getUpperBounds());
            }

            @Override
            void visitParameterizedType(ParameterizedType type) {
                visit(type.getActualTypeArguments());
                visit(type.getOwnerType());
            }

            @Override
            void visitGenericArrayType(GenericArrayType type) {
                visit(type.getGenericComponentType());
            }
        }.visit(runtimeType);
        return this;
    }

    private boolean someRawTypeIsSubclassOf(Class<?> superclass) {
        for (Class<?> rawType : getRawTypes()) {
            if (superclass.isAssignableFrom(rawType)) {
                return true;
            }
        }
        return false;
    }

    private boolean isSubtypeOfParameterizedType(ParameterizedType supertype) {
        Class<?> matchedClass = of(supertype).getRawType();
        if (!someRawTypeIsSubclassOf(matchedClass)) {
            return false;
        }
        Type[] typeParams = matchedClass.getTypeParameters();
        Type[] toTypeArgs = supertype.getActualTypeArguments();
        for (int i = 0; i < typeParams.length; i++) {
            // If 'supertype' is "List<? extends CharSequence>"
            // and 'this' is StringArrayList,
            // First step is to figure out StringArrayList "is-a" List<E> and <E> is
            // String.
            // typeParams[0] is E and fromTypeToken.get(typeParams[0]) will resolve to
            // String.
            // String is then matched against <? extends CharSequence>.
            if (!resolveType(typeParams[i]).is(toTypeArgs[i])) {
                return false;
            }
        }
        // We only care about the case when the supertype is a non-static inner class
        // in which case we need to make sure the subclass's owner type is a subtype of the
        // supertype's owner.
        return Modifier.isStatic(((Class<?>) supertype.getRawType()).getModifiers()) || supertype.getOwnerType() == null
                || isOwnedBySubtypeOf(supertype.getOwnerType());
    }

    private boolean isSubtypeOfArrayType(GenericArrayType supertype) {
        if (runtimeType instanceof Class) {
            Class<?> fromClass = (Class<?>) runtimeType;
            if (!fromClass.isArray()) {
                return false;
            }
            return of(fromClass.getComponentType()).isSubtypeOf(supertype.getGenericComponentType());
        } else if (runtimeType instanceof GenericArrayType) {
            GenericArrayType fromArrayType = (GenericArrayType) runtimeType;
            return of(fromArrayType.getGenericComponentType()).isSubtypeOf(supertype.getGenericComponentType());
        } else {
            return false;
        }
    }

    private boolean isSupertypeOfArray(GenericArrayType subtype) {
        if (runtimeType instanceof Class) {
            Class<?> thisClass = (Class<?>) runtimeType;
            if (!thisClass.isArray()) {
                return thisClass.isAssignableFrom(Object[].class);
            }
            return of(subtype.getGenericComponentType()).isSubtypeOf(thisClass.getComponentType());
        } else if (runtimeType instanceof GenericArrayType) {
            return of(subtype.getGenericComponentType())
                    .isSubtypeOf(((GenericArrayType) runtimeType).getGenericComponentType());
        } else {
            return false;
        }
    }

    /**
     * Return true if any of the following conditions is met:
     *
     * <ul>
     * <li>'this' and {@code formalType} are equal
     * <li>{@code formalType} is {@code <? extends Foo>} and 'this' is a subtype of {@code Foo}
     * <li>{@code formalType} is {@code <? super Foo>} and 'this' is a supertype of {@code Foo}
     * </ul>
     */
    private boolean is(Type formalType) {
        if (runtimeType.equals(formalType)) {
            return true;
        }
        if (formalType instanceof WildcardType) {
            // if "formalType" is <? extends Foo>, "this" can be:
            // Foo, SubFoo, <? extends Foo>, <? extends SubFoo>, <T extends Foo> or
            // <T extends SubFoo>.
            // if "formalType" is <? super Foo>, "this" can be:
            // Foo, SuperFoo, <? super Foo> or <? super SuperFoo>.
            return every(((WildcardType) formalType).getUpperBounds()).isSupertypeOf(runtimeType)
                    && every(((WildcardType) formalType).getLowerBounds()).isSubtypeOf(runtimeType);
        }
        return false;
    }

    private static Bounds every(Type[] bounds) {
        // Every bound must match. On any false, result is false.
        return new Bounds(bounds, false);
    }

    private static Bounds any(Type[] bounds) {
        // Any bound matches. On any true, result is true.
        return new Bounds(bounds, true);
    }

    private static class Bounds {
        private final Type[] bounds;
        private final boolean target;

        Bounds(Type[] bounds, boolean target) {
            this.bounds = bounds;
            this.target = target;
        }

        boolean isSubtypeOf(Type supertype) {
            for (Type bound : bounds) {
                if (of(bound).isSubtypeOf(supertype) == target) {
                    return target;
                }
            }
            return !target;
        }

        boolean isSupertypeOf(Type subtype) {
            TypeToken<?> type = of(subtype);
            for (Type bound : bounds) {
                if (type.isSubtypeOf(bound) == target) {
                    return target;
                }
            }
            return !target;
        }
    }

    private ImmutableSet<Class<? super T>> getRawTypes() {
        final ImmutableSet.Builder<Class<?>> builder = ImmutableSet.builder();
        new TypeVisitor() {
            @Override
            void visitTypeVariable(TypeVariable<?> t) {
                visit(t.getBounds());
            }

            @Override
            void visitWildcardType(WildcardType t) {
                visit(t.getUpperBounds());
            }

            @Override
            void visitParameterizedType(ParameterizedType t) {
                builder.add((Class<?>) t.getRawType());
            }

            @Override
            void visitClass(Class<?> t) {
                builder.add(t);
            }

            @Override
            void visitGenericArrayType(GenericArrayType t) {
                builder.add(Types.getArrayClass(of(t.getGenericComponentType()).getRawType()));
            }
        }.visit(runtimeType);
        // Cast from ImmutableSet<Class<?>> to ImmutableSet<Class<? super T>>
        @SuppressWarnings({"unchecked", "rawtypes"})
        ImmutableSet<Class<? super T>> result = (ImmutableSet) builder.build();
        return result;
    }

    private boolean isOwnedBySubtypeOf(Type supertype) {
        for (TypeToken<?> type : getTypes()) {
            Type ownerType = type.getOwnerTypeIfPresent();
            if (ownerType != null && of(ownerType).isSubtypeOf(supertype)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns the owner type of a {@link ParameterizedType} or enclosing class of a {@link Class},
     * or null otherwise.
     */
    @Nullable
    private Type getOwnerTypeIfPresent() {
        if (runtimeType instanceof ParameterizedType) {
            return ((ParameterizedType) runtimeType).getOwnerType();
        } else if (runtimeType instanceof Class<?>) {
            return ((Class<?>) runtimeType).getEnclosingClass();
        } else {
            return null;
        }
    }

    /**
     * Returns the type token representing the generic type declaration of {@code cls}. For example:
     * {@code TypeToken.getGenericType(Iterable.class)} returns {@code Iterable<T>}.
     *
     * <p>
     * If {@code cls} isn't parameterized and isn't a generic array, the type token of the class is
     * returned.
     */
    @VisibleForTesting
    static <T> TypeToken<? extends T> toGenericType(Class<T> cls) {
        if (cls.isArray()) {
            Type arrayOfGenericType = Types.newArrayType(
                    // If we are passed with int[].class, don't turn it to GenericArrayType
                    toGenericType(cls.getComponentType()).runtimeType);
            @SuppressWarnings("unchecked") // array is covariant
            TypeToken<? extends T> result = (TypeToken<? extends T>) of(arrayOfGenericType);
            return result;
        }
        TypeVariable<Class<T>>[] typeParams = cls.getTypeParameters();
        Type ownerType = cls.isMemberClass() && !Modifier.isStatic(cls.getModifiers())
                ? toGenericType(cls.getEnclosingClass()).runtimeType
                : null;

        if ((typeParams.length > 0) || ((ownerType != null) && ownerType != cls.getEnclosingClass())) {
            @SuppressWarnings("unchecked") // Like, it's Iterable<T> for Iterable.class
            TypeToken<? extends T> type =
                    (TypeToken<? extends T>) of(Types.newParameterizedTypeWithOwner(ownerType, cls, typeParams));
            return type;
        } else {
            return of(cls);
        }
    }

    private TypeToken<? super T> getSupertypeFromUpperBounds(Class<? super T> supertype, Type[] upperBounds) {
        for (Type upperBound : upperBounds) {
            @SuppressWarnings("unchecked") // T's upperbound is <? super T>.
            TypeToken<? super T> bound = (TypeToken<? super T>) of(upperBound);
            if (bound.isSubtypeOf(supertype)) {
                @SuppressWarnings({"rawtypes", "unchecked"}) // guarded by the isSubtypeOf check.
                TypeToken<? super T> result = bound.getSupertype((Class) supertype);
                return result;
            }
        }
        throw new IllegalArgumentException(supertype + " isn't a super type of " + this);
    }

    private TypeToken<? extends T> getSubtypeFromLowerBounds(Class<?> subclass, Type[] lowerBounds) {
        for (Type lowerBound : lowerBounds) {
            @SuppressWarnings("unchecked") // T's lower bound is <? extends T>
            TypeToken<? extends T> bound = (TypeToken<? extends T>) of(lowerBound);
            // Java supports only one lowerbound anyway.
            return bound.getSubtype(subclass);
        }
        throw new IllegalArgumentException(subclass + " isn't a subclass of " + this);
    }

    private TypeToken<? super T> getArraySupertype(Class<? super T> supertype) {
        // with component type, we have lost generic type information
        // Use raw type so that compiler allows us to call getSupertype()
        @SuppressWarnings("rawtypes")
        TypeToken componentType = checkNotNull(getComponentType(), "%s isn't a super type of %s", supertype, this);
        // array is covariant. component type is super type, so is the array type.
        @SuppressWarnings("unchecked") // going from raw type back to generics
        TypeToken<?> componentSupertype = componentType.getSupertype(supertype.getComponentType());
        @SuppressWarnings("unchecked") // component type is super type, so is array type.
        TypeToken<? super T> result = (TypeToken<? super T>)
        // If we are passed with int[].class, don't turn it to GenericArrayType
        of(newArrayClassOrGenericArrayType(componentSupertype.runtimeType));
        return result;
    }

    private TypeToken<? extends T> getArraySubtype(Class<?> subclass) {
        // array is covariant. component type is subtype, so is the array type.
        TypeToken<?> componentSubtype = getComponentType().getSubtype(subclass.getComponentType());
        @SuppressWarnings("unchecked") // component type is subtype, so is array type.
        TypeToken<? extends T> result = (TypeToken<? extends T>)
        // If we are passed with int[].class, don't turn it to GenericArrayType
        of(newArrayClassOrGenericArrayType(componentSubtype.runtimeType));
        return result;
    }

    private Type resolveTypeArgsForSubclass(Class<?> subclass) {
        // If both runtimeType and subclass are not parameterized, return subclass
        // If runtimeType is not parameterized but subclass is, process subclass as a parameterized
        // type
        // If runtimeType is a raw type (i.e. is a parameterized type specified as a Class<?>), we
        // return subclass as a raw type
        if (runtimeType instanceof Class
                && ((subclass.getTypeParameters().length == 0) || (getRawType().getTypeParameters().length != 0))) {
            // no resolution needed
            return subclass;
        }
        // class Base<A, B> {}
        // class Sub<X, Y> extends Base<X, Y> {}
        // Base<String, Integer>.subtype(Sub.class):

        // Sub<X, Y>.getSupertype(Base.class) => Base<X, Y>
        // => X=String, Y=Integer
        // => Sub<X, Y>=Sub<String, Integer>
        TypeToken<?> genericSubtype = toGenericType(subclass);
        @SuppressWarnings({"rawtypes", "unchecked"}) // subclass isn't <? extends T>
        Type supertypeWithArgsFromSubtype = genericSubtype.getSupertype((Class) getRawType()).runtimeType;
        return new TypeResolver().where(supertypeWithArgsFromSubtype, runtimeType)
                .resolveType(genericSubtype.runtimeType);
    }

    /**
     * Creates an array class if {@code componentType} is a class, or else, a
     * {@link GenericArrayType}. This is what Java7 does for generic array type parameters.
     */
    private static Type newArrayClassOrGenericArrayType(Type componentType) {
        return Types.JavaVersion.JAVA7.newArrayType(componentType);
    }

    private static final class SimpleTypeToken<T> extends TypeToken<T> {

        SimpleTypeToken(Type type) {
            super(type);
        }

        private static final long serialVersionUID = 0;
    }

    /**
     * Collects parent types from a sub type.
     *
     * @param <K> The type "kind". Either a TypeToken, or Class.
     */
    private abstract static class TypeCollector<K> {

        static final TypeCollector<TypeToken<?>> FOR_GENERIC_TYPE = new TypeCollector<TypeToken<?>>() {
            @Override
            Class<?> getRawType(TypeToken<?> type) {
                return type.getRawType();
            }

            @Override
            Iterable<? extends TypeToken<?>> getInterfaces(TypeToken<?> type) {
                return type.getGenericInterfaces();
            }

            @Nullable
            @Override
            TypeToken<?> getSuperclass(TypeToken<?> type) {
                return type.getGenericSuperclass();
            }
        };

        static final TypeCollector<Class<?>> FOR_RAW_TYPE = new TypeCollector<Class<?>>() {
            @Override
            Class<?> getRawType(Class<?> type) {
                return type;
            }

            @Override
            Iterable<? extends Class<?>> getInterfaces(Class<?> type) {
                return Arrays.asList(type.getInterfaces());
            }

            @Nullable
            @Override
            Class<?> getSuperclass(Class<?> type) {
                return type.getSuperclass();
            }
        };

        /** For just classes, we don't have to traverse interfaces. */
        final TypeCollector<K> classesOnly() {
            return new ForwardingTypeCollector<K>(this) {
                @Override
                Iterable<? extends K> getInterfaces(K type) {
                    return ImmutableSet.of();
                }

                @Override
                ImmutableList<K> collectTypes(Iterable<? extends K> types) {
                    ImmutableList.Builder<K> builder = ImmutableList.builder();
                    for (K type : types) {
                        if (!getRawType(type).isInterface()) {
                            builder.add(type);
                        }
                    }
                    return super.collectTypes(builder.build());
                }
            };
        }

        final ImmutableList<K> collectTypes(K type) {
            return collectTypes(ImmutableList.of(type));
        }

        ImmutableList<K> collectTypes(Iterable<? extends K> types) {
            // type -> order number. 1 for Object, 2 for anything directly below, so on so forth.
            Map<K, Integer> map = Maps.newHashMap();
            for (K type : types) {
                collectTypes(type, map);
            }
            return sortKeysByValue(map, Ordering.natural().reverse());
        }

        /** Collects all types to map, and returns the total depth from T up to Object. */
        @CanIgnoreReturnValue
        private int collectTypes(K type, Map<? super K, Integer> map) {
            Integer existing = map.get(type);
            if (existing != null) {
                // short circuit: if set contains type it already contains its supertypes
                return existing;
            }
            // Interfaces should be listed before Object.
            int aboveMe = getRawType(type).isInterface() ? 1 : 0;
            for (K interfaceType : getInterfaces(type)) {
                aboveMe = Math.max(aboveMe, collectTypes(interfaceType, map));
            }
            K superclass = getSuperclass(type);
            if (superclass != null) {
                aboveMe = Math.max(aboveMe, collectTypes(superclass, map));
            }
            /*
             * TODO(benyu): should we include Object for interface? Also, CharSequence[] and
             * Object[] for String[]?
             *
             */
            map.put(type, aboveMe + 1);
            return aboveMe + 1;
        }

        private static <K, V> ImmutableList<K> sortKeysByValue(final Map<K, V> map,
                final Comparator<? super V> valueComparator) {
            Ordering<K> keyOrdering = new Ordering<K>() {
                @Override
                public int compare(K left, K right) {
                    return valueComparator.compare(map.get(left), map.get(right));
                }
            };
            return keyOrdering.immutableSortedCopy(map.keySet());
        }

        abstract Class<?> getRawType(K type);

        abstract Iterable<? extends K> getInterfaces(K type);

        @Nullable
        abstract K getSuperclass(K type);

        private static class ForwardingTypeCollector<K> extends TypeCollector<K> {

            private final TypeCollector<K> delegate;

            ForwardingTypeCollector(TypeCollector<K> delegate) {
                this.delegate = delegate;
            }

            @Override
            Class<?> getRawType(K type) {
                return delegate.getRawType(type);
            }

            @Override
            Iterable<? extends K> getInterfaces(K type) {
                return delegate.getInterfaces(type);
            }

            @Override
            K getSuperclass(K type) {
                return delegate.getSuperclass(type);
            }
        }
    }
}
